U.S. Pat. No. 3,393,425 discloses a pelletizer in which the plastic material to be pelletized is plasticized by means of an extruder, and thereafter extruded in the form of strands through a die plate. After leaving the die plate, the strands are cut into short pieces by means of rotating cutting knives arranged parallel to the die plate and cooled by means of air or a water bath in order to prevent the pellets from sticking together.
The cutting knives rotating in front of the die plate are mounted on one or several cutting beams. The cutting beams are fixed on a single central shaft that is rotated by means of a motor so that the cutting knives rotate in front of the die plate at a very small distance therefrom and cut and/or pelletize the strands leaving the die plate.
The distance between the rotating cutting, knives and the die plate must not exceed 50-150 My (0.001 mm) in order to obtain a smooth cut. If the distance is greater, the cut pellets will have beards and/or small threads that destroy the free-flowing properties and thus the possibility of metering the pellets, thus rendering a further processing of the pellets more difficult.
When the distance is too great, threads are formed at the pellets, and when it is too small, the wear of the rotating cutting knives is increased to an extent which cannot be tolerated.